In frontier industries such as the semiconductor manufacturing industry and liquid crystal manufacturing industry, controlling pollution of air and product surfaces in clean rooms is important to ensure a high yield, high quality, and product reliability. In the semiconductor manufacturing industry, in particular, as the degree of integration of the products increases, control of ionized gaseous pollutants has become indispensable in addition to the control of particulate matters using a HEPA filter, ULPA, and the like.
The ionized gaseous pollutants include basic gases and acidic gases. Of these gases, the basic gases such as ammonia are known to adversely affect resolution during the step of exposure to radiation and cause wafer surfaces to become clouded in the manufacture of semiconductor devices. SOX, which is an acidic gas, produces lamination defects in substrates in the thermal oxidation film-forming process during manufacture of semiconductors, whereby the characteristics and reliability of the semiconductor devices are adversely affected.
Since ionized gaseous pollutants cause various problems in semiconductor manufacturing processes and the like in this manner, it is demanded to reduce the concentration of the ionized gaseous pollutants in a clean room used in semiconductor manufacturing and the like to a concentration of several μg/m3 or less.
A conventional practice for removing the ionized gaseous pollutants has been to introduce ion-exchange groups into a chemical filter. Japanese Patent Application Laid-open No. 2001-259339 (Patent Document 1) discloses an air filter material made of paper comprising a matrix and ion-exchange resin powder having a particle size and ion-exchange capacity in specific ranges incorporated into the matrix.
Japanese Patent Application Laid-open No. 2000-5544 (Patent Document 2) discloses a deodorant comprising an adsorption medium and an ion-exchange resin.
Japanese Patent Application Laid-open No. 2003-10613 (Patent Document 3) discloses an air filter medium for filtering ionized alkaline gases, wherein the substrate of the filter medium contains fine particles, granules, or fiber made of a cation-exchange resin, on which phosphoric acid is supported.
In addition to the initial target performance of eliminating ionized gaseous pollutants to a concentration of several μg/m3 or less, the air filter is required to possess excellent durability, specifically, to exhibit elimination performance for a long period of time. Therefore, a large amount of ion-exchange resin must be introduced to increase the ion-exchange capacity per unit volume of the chemical filter.
However, in the air filter material described in Japanese Patent Application Laid-open No. 2001-259339, if a large amount of fine particles of ion-exchange resin is attached to the pulp matrix, the fine particles of ion-exchange resin are easily detached from the matrix because the fine particles are retained on the surface of the matrix by means of an electrostatic force or frictional force between the pulp matrix and the fine particles of ion-exchange resin.
The deodorant described in Japanese Patent Application Laid-open No. 2000-5544 comprises a mixture of activated carbon and an ion-exchange resin milled into paper. Since an increased amount of the ion-exchange resin mixed with activated carbon unduly impairs the strength of the resulting deodorant obtained by paper-milling, the deodorant may collapse during aeration or milling of the paper is impossible.
The air filter material described in Japanese Patent Application Laid-open No. 2003-10613 has the same problem of difficulty in incorporating a large amount of ion-exchange resin into the filter substrate as the deodorant of Japanese Patent Application Laid-open No. 2000-5544. In addition, since the filter material can eliminate ionized gaseous pollutants by the neutralization reaction of phosphoric acid supported on the air filter with the ionized gaseous pollutants, the salt generated by the neutralization reaction may inhibit processed gas from diffusing in spaces in filter fibers, which results in a decrease in the life of the filter material.
An object of the present invention is, therefore, to provide a chemical filter possessing a large ion-exchange capacity per unit volume, exhibiting high initial performance of eliminating ionized gaseous pollutants, and exhibiting excellent durability in elimination performance.